1. Field of the Invention
This invention relates to a dye developer for photography, and particularly to a dye developer used in a photographic material to form an image by the diffusion transfer process. More particularly the present invention relates to a dye developer which at the step of image exposure absorbs light at a short wavelength region so that the spectral sensitivity of the photographic emulsion used in combination therewith is not disturbed, and whose absorption is shifted to a desired, longer wavelength region by reaction with a processing agent.
2. Description of the Prior Art
A diffusion transfer process utilizing a dye developer is well known in the photographic art (for example, as disclosed in U.S. Pat. Nos. 2,983,606, 3,134,764, 3,188,209, 3,255,001, 3,316,090 and 3,345,163).
The dye developer, as noted in U.S. Pat. Nos. 2,983,606, 3,134,764, 3,188,209, 3,255,001, 3,316,090 and 3,345,163, is a compound which contains, in the same molecule, both a group capable of developing a silver halide and a chromophoric system of a dye, and which can be immobilized depending on the amount of silver halide developed, and of which the residual amount can be transferred to an image-receiving layer to form transferred dye images.
The absorption caused by such a dye developer often overlaps the spectrally sensitized region of the photographic emulsion used in combination therewith. Hence the sensitivity of the emulsion is apparently reduced, when the dye developer is incorporated in the sensitized emulsion layer or when the dye developer layer is arranged contiguous to the emulsion layer and in such a manner that image exposure is made through the dye developer layer.
U.S. Pat. Nos. 3,307,947 and 3,579,334 disclose a modified method to eliminate this problem described above. This method employs a dye developer whose absorption is temporarily shifted to a shorter wavelength region and whose desired colored form is restored upon reaction with a processing agent. Unfortunately the same patents disclose magenta color developers. U.S. Pat. No. 3,230,085 also discloses yellow dye developers based on a similar concept, but the carboxylic acid groups of the compounds disclosed in this patent are regenerated by the action of an alkaline material contained in the processing agent, and the presence of the carboxylic acid groups causes an imperfect immobilization of the quinone derivatives formed at the exposed area as the result of reduction of silver ion to silver, thus resulting in a slight "leakage" (transfer of a slight amount of dye) at the highlight area. The "temporary blue shift" i.e., toward a shorter wavelength, of a dye developer described above is generally achieved by the acylation of a hydroxyl or an amino group which is an auxochromic group of an azo dye. An azo dye can exist in either of two tautomeric isomers, the hydrazono form and the azo form. The hydrazono form absorbs longer wavelength light than the azo form, and the acylation is considered to fix the molecule in the azo form, thus achieving the blue shift. Unfortunately, many of the yellow azo dyes exhibiting desirable absorption characteristics such as, for example, pyrazoloneazo, 3-arylazo-2,4 -dihydroxyquinoline, 2-arylazo-1,3-indane-dione dyes, etc., cannot be acylated at all or can be acylated only with great difficulty. Further, in the case of pyrazolobenzimidazoleazo or pyrimidazoloneazo dyes, some dyes exhibit only insufficient blue shift upon acylation, or in the case of dyes containing an aniline nucleus, the color of the acylated derivatives is not restored by the processing agent.
Thus there are very few examples of compounds which meet all of the requirements for the present invention, i.e., (1) a desirable absorption as a yellow dye after color restoration; (2) an absorption shift to a sufficiently short wavelength region as a temporary blue shift; (3) rapid color restoration by a processing agent; and (4) perfect inhibition of color restoration during storage of the photographic material. Although the compounds described in Japanese patent application No. 76226/1973 satisfy the above-described requirements fairly well, they still suffer from the shortcomings of poor solubility, low transfer efficiency and particularly unsatisfactory absorption characteristics, i.e., absorption at a too short wavelength region after color restoration, when used in a diffusion transfer material.